This invention relates to a bicycle pedal mechanism, with a variable leverage pedal crank.
French Pat. No. 2365474, German Pat. No. 272204, Swiss Pat. No. 598050, U.S. Pat. No. 4,125,239 and French Pat. No. 226507 have disclosed various pedal mechanisms with telescopically or radially movable pedal cranks. In these mechanisms, telescoping movement of a crank is obtained by arrangements of sleeves, springs, sliding pieces and the like, while radial movement of a crank is achieved by a cam, planetary gears and a guide pulley with a large circular orbit.
These mechanisms are all complicated in construction and have large frictional losses. In addition, it is hard for such mechansims to pass through the knee point generated by an eccentric mechansim used therein. For example, in French Pat. No. 2365474, since a guide pulley with a large circular orbit must be fixed on the outside of the chain sprocket in order to carry out both rotation of a pedal and radial movement of a pedal crank, the width of the bicycle in the direction of the bottom or lower bracket bearing axle is increased. The diameter of the guide pulley is 350 mm and the frictional loss is large for a bearing ball sliding on such a large orbit. Furthermore, no arrangement is provided to ensure that the pedal crank pases through the knee point generated by an eccentric mechanism thereof so that it is hard for a bicycle to start and maintain operation.